Such as, apparently, sleeping in the same bed as your partner. Dr Neil Stanley, a sleep specialist, says: "Historically, we have never been meant to sleep in the same bed as each other. It is a bizarre thing to do." More worringly, or maybe not, there is the suggestion that sleeping (not even having sex) with someone else drains men's brains. Now, there's a thought for a story - even better than Stephen King's idea of sleeping on Lovecraft's Pillow.
And my writing prompt for today is: 'Sleep is selfish'